Alison Whitney’s old ride, a lumbering two-door Pontiac in battleship gray, had all the charm of a truck stop bathroom. Dumping that heap was as easy as discarding a well-chewed wad of Dubble Bubble.

Agreeing to commute by bike for a year in car-crazed San Diego? That was a whole ’nother stick of gum. “It is not as convenient,” admitted Whitney, a University Heights resident. “But once you are forced into a situation where your word is your bond, you follow through.”

Since last fall, Whitney has accepted the occasional lift from her boyfriend and co-workers. But these are exceptions to a strenuous rule. Whitney is the 2011 San Diego winner of a Colorado brewery’s car-for-bike swap, a highlight of the annual Tour de Fat. This traveling bicycle-and-beer-themed carnival sponsored by New Belgium Brewing, maker of Fat Tire ale, returns here on Sept. 29 — when a new “swapper” will be announced.

Whitney, 38, is part of a small but expanding subculture. Using data from the 2010 census, the League of American Bicyclists estimates that little more than .5 percent of all American workers commute on two wheels. The numbers are higher in college towns, especially in the West — Davis leads with a 22.1 percent rate, while Boulder, home to the University of Colorado, is within a spoke of 10 percent. San Diego’s 1 percent, while modest, represents nearly a 100 percent increase since 2000. This trend seems destined to continue, as local cities have recently added bike lanes, bike parking “corrals” and adopted other bike-friendly policies.

“We live in a perfect place to ride your bike for transportation,” said Andy Hanshaw, executive director of the San Diego Bicycle Coalition. “People want to save money on gas, do something good for the environment and be healthier.”

Yet bicycling — like driving — can be lethal. In a single month this summer, one local biker died when he was struck by a car; another after losing control on a steep mountain road; and a third when his front wheel fell off, catapulting the helmetless rider headfirst onto the pavement. There’s also the risk of being “doored,” slamming into a door thrown open by a parked motorist.

The two-wheeled life has its risks, but Whitney insists the rewards are greater. She remembers a scene from her driving days, mired in bumper-to-bumper traffic. Going nowhere, she had time to study the bicyclists breezing down an adjacent trail.

“Gee,” she thought, “they are moving at their own pace, moving because they want to. They’re not stuck in traffic.”

If her daily commute now involves pedaling up a steep hill — Washington Avenue into Mission Hills, say — at least she’s never stuck.

Hauling an accordion

Before each stop in the Tour de Fat — this year, San Diego is the 13th stop on the tour’s 15-city itinerary — the brewery reviews essays and videos from locals who insist they are eager to abandon internal combustion engines for pedal-power. In 2010, the San Diego recipient was Gabe Kreb, then a 27-year-old musician and part-time big top performer.

“I was working for Technomania Circus in Barrio Logan,” said Kreb, who now lives in Portland. “The Tour de Fat is a bit of a circus itself, so they liked that aspect.”

Kreb, like Whitney, had been saddled with a car that was a reliable as a toddler’s sense of balance. Trading that ‘94 Saturn SL for a new Black Sheep touring bike was a joy, even if the latter needed a critical modification.

“I installed a rear rack,” Kreb said, “so I could haul my accordion. It was the best bike I’ve ever owned, and I’ve owned a few bikes.”

Last fall, Whitney succeeded Kreb. On the Tour de Fat’s stage, she handed her car keys to a New Belgium employee. In exchange, she received a sturdy 11-speed, also from Black Sheep.

Within days, a tow truck hauled away her Pontiac. That clunker was auctioned off, with all proceeds donated to local biking groups.

From that moment on, Whitney’s life required a little more planning. She sought, and found, jobs within biking distance of her University Heights home. The IT company that now employs her is in Old Town, six miles from home; on days she reports to a part-time sales job with the Crate & Barrel in Mission Valley, her commute is another four miles.

She packs clean business attire in the bike’s waterproof panniers. She plots out routes with the least car traffic. The bike has a front light, a flashing rear light, reflecting strips on the tires and the pedals; she straps reflecting material around her ankles and wears a helmet and a bracelet listing her identify and blood type. Some days, all these precautions seem insufficient.

Once, a driver — she was texting — almost clobbered Whitney. Another morning, she was near work when a car came within inches of a collision. Whitney parked, locked her bike and then got into the office building’s elevator — where she was joined by the driver who had nearly squashed her.

“Oh, man,” he said, “I’m glad you signaled. I almost didn’t see you!”

Most people, though, have been aware — and encouraging. “Everybody has been so supportive of my biking,” she said. “It’s awesome.”

Fire with fire

If every bicyclist can recite horror stories about clueless motorists, many drivers gripe about reckless bicyclists who run stop lights or pedal into oncoming traffic. In June, the monthly Critical Mass bicycle ride cruised down the Mission Beach boardwalk, where one biker shoved a female pedestrian onto the concrete. The resulting brawl, while brief, left the woman and her husband with cuts and bruises.

Many veteran bicyclists have their own scars, physical and psychological, from death-defying encounters on the road.

Tour de Fat

WHEN: Sept. 29, 10 a.m. to 4:30 p.m.

WHERE: Golden Hill Park, Golden Hill Drive, San Diego

ADMISSION: Free

ENTERING THE CAR-FOR-BIKE SWAP: Send essays to trademycarforabik... or post a video (two minutes or less) on the New Belgium Tour de Fat Facebook page

“You have some bicyclists who want to fight fire with fire, who take things to extremes,” Whitney said. “That’s not uniting.”

The Tour de Fat, though, steers around these thorny issues like so many potholes. The day, which includes a parade of costumed bicyclists through South Park and live, kid-appropriate entertainment, celebrates the two-wheeled lifestyle.

“It’s sheer fun,” said Hanshaw, who will wear his Elvis costume. (“The King on wheels,” he explained.)

It’s also a day when a simple exchange will change someone’s life. For the better, insists Whitney.

“I’m proof that you can do it in our town,” she said, “with all of our sprawl.”